The present invention relates to a lens for an optical pick-up and an optical pick-up for an optical disc drive employing the lens.
An optical disc drive which reads information from an optical disc, such as CD or DVD, has an optical pick-up. The optical pick-up includes a laser source and a lens which converges a laser beam emitted by the laser source onto the optical disc.
In general, a lens employed in an optical pick-up is made of resin. That is, the lens is a resin product formed by injection molding. Therefore, it is necessary to remove a gate part from the molded lens. Japanese Patent Provisional Publication No. 2009-181033A (hereafter, referred to as JP2009-181033A) discloses an example of a conventional lens from which a gate part has removed. JP2009-181033A discloses also a method for removing a gate part from a lens. FIG. 5A is a top view of a conventional lens 201, and FIG. 5B is a cross section of the lens 201 viewed along a line A-A in FIG. 5A. In the following, directions are defined based on FIG. 5B. Specifically, a direction of an optical axis of the lens 201 is defined as an up-and-down direction, a side on which a first lens surface 211 is formed is defined as an “upper side”, and a side on which a second lens surface 212 is formed is defined as a “lower side”.
The lens 201 shown in FIGS. 5A and 5B includes a flange part 220. The flange part 220 is formed to protrude from peripheries of the first lens surface 211 (i.e., an optical disc side) and the second lens surface 212 (i.e., a light source side). At an edge part of a lower surface 221 of the flange part 220, an installation surface 221a is formed to be recessed upward (i.e., to the optical disc side).
A gate part go of the lens 201 is formed to extend from a cylindrical outer circumferential surface 222 of the flange part 220 in a radially outward direction (i.e., the gate part go extends from the upper side to the lower side in FIG. 5A). The gate part go is cut off by moving an endmill along a direction (i.e., a left and right direction in FIG. 5A) perpendicular to both of a radial direction of the lens 201 (i.e., a direction pointing from the gate part go to the center of the lens 201) and a direction of an optical axis of the lens 201. To completely cut off the gate part go, a part of the cylindrical outer circumferential surface 222 of the flange part 220 is also cut off (i.e., a s-called D-cutting).
In general, a lens is fixed to a holder of an optical pick-up with an adhesive. FIG. 6A is a top view illustrating a general configuration of a holder 101 of an optical pick-up, and FIG. 6B is a cross section of the holder 101 in which the lens 201 is installed (a cross section viewed along a line B-B in FIG. 6A).
As shown in FIGS. 6A and 6B, the holder 101 is a plate-like member, and a circular through hole 111 for accommodating the lens 201 is formed in the holder 101 to extend from an upper surface 102a to a lower surface 102b. On a cylindrical inner surface of the through hole 111, three projections 121 are provided at intervals of 120 degrees with respect to a center axis ax. Each of the projections 121 is formed in a shape of a flange to protrude toward the center axis ax. At a part on the upper surface 102a situated next to each projection 121, an adhesion catch 131 is formed to protrude upward from the upper surface 102a to have a form of a letter “U”. That is, three adhesion catches 131 are provided. When the lens 201 is installed on the holder 101, the installation surface 221a of the lens 201 contacts upper surfaces of the projections 121 (see FIG. 6B).
In the state where the installation surface 221a of the lens 201 is placed on the projections 121 of the holder 101, parts of the cylindrical outer circumferential surface 222 of the flange part 220 face the adhesion catches 131, respectively. Therefore, at each adhesion catch 131, a recessed part sa for adhesion (see FIG. 6B) is formed between an inner face 131 a of the adhesion catch 131 and the cylindrical outer circumferential surface 222 of the lens 201. By injecting an adhesion to each recessed part sa and by letting the adhesion harden, the lens 201 is fixed to the holder 101.